Recent advances in process and adsorbent technology have enabled traditional large-scale pressure swing adsorption (PSA) systems to be scaled down to much smaller systems that operate in rapid cycles of very short duration. These small, rapid-cycle PSA systems may be utilized, for example, in portable medical oxygen concentrators that recover oxygen from ambient air. As the market for these concentrators grows, there is an incentive to develop increasingly smaller, lighter, and more portable units for the benefit of patients on oxygen therapy.
The impact of feed gas impurities on the adsorbent is a generic problem in many PSA systems, and the impact is especially serious in the small adsorbent beds required in small rapid-cycle PSA systems. For example, the water and carbon dioxide impurities in air can cause a significant decline in the performance of small PSA air separation systems by progressive deactivation of the adsorbent due to adsorbed impurities that are incompletely removed during regeneration steps of the PSA cycle. Because of this progressive deactivation, oxygen recovery will decline over time and adsorbent replacement may be required on a regular basis. Alternatively, the adsorbent beds may have to be oversized to account for progressive adsorbent deactivation. Both of these situations are undesirable because they increase the cost and weight of the oxygen concentrator system.
There is a need in the art for improved methods to remove impurities, particularly water, in the design and operation of small, portable, rapid-cycle PSA oxygen concentrators. This need is addressed by the embodiments of the invention described below and defined by the claims that follow.